Sigmatropic rearrangements of alkyl groups

Sigmatropic Rearrangements of Alkyl Group 93 3.8.1 Solved Problems 144... 

When an alkyl group migrates, there is an additional stereochemical feature to consider. The shift can occur with retention or inversion at the migrating center. The analysis of sigmatropic shifts of alkyl groups is illustrated in Fig. 11.7. The allowed processes include the suprafacial 1,3-shift with inversion and the suprafacial 1,5-shift with retention. Sigmatropic rearrangements of order [3,3] are very common ... 

Another class of reactions that can occur by sigmatropic rearrangements involve alkyl group shifts ... 

Piers and Ruediger have smartly used this basic reaction (equation 168) for a synthesis of the sesquiterpenoid -himachalene ". However, loading the systems to be rearranged with alkyl groups can considerably decelerate the Cope process with the result of competing homo[l, 5]-sigmatropic hydrogen shift in the trans compounds (equation... 

Common error alert A mechanism involving a [1,3] sigmatropic rearrangement of an alkyl group, though not impossible, should be viewed with suspicion. 

Thermal and mercury(ii)-catalysed [3,3]sigmatropic rearangement of allylic trichloroacetimidates and allylic pseudo-ureas" e.g. geraniol, linalool) are useful for the 1,3-transposition of hydroxy- and amino-groups the former is synthetically preferred. The [2,3]sigmatropic rearrangement of allylic sulphoxides has been used to effect an alkylative 1,3-carbonyl transposition of enones (e.g. carvone). ... 

Alkylation of the lithium enolate of 800 with 799 gives 801 as an inseparable 1 1 mixture of C-3 diastereomers. [2,3]-Sigmatropic rearrangement of 801 occurs upon treatment with MSH followed by triethyl phosphite. Protection of the newly formed amine is accomplished in situ with benzyl chloroformate in the presence of sodium bicarbonate. The rearrangement occurs with 85% chirality transfer and concomitant loss of the TMS protecting group. 

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